Delhi Police Commissioner BS Bassi on Thursday joined the probe into murder of his mother Sunanda Pushkar.
Shiv Menon appeared before the Special Investigation Team at its office and was questioned in connection with the murder case.
Menon reached the Vasant Vihar police station, also the office of the SIT, at around 1.15 pm.
Bassi later said Menon has joined the investigation, which is under progress. He added that Menon is likely to throw light on many aspects in the case.
Menon was not questioned earlier as he was out of India.
A police team probing the murder of Sunanda has questioned at least 15 people in connection with the case so far.
Congress MP Shashi Tharoor, his staff members and close friends were among those quizzed by the Delhi Police.
Former Samajwadi Party leader Amar Singh and senior journalist Nalini Singh have also been questioned by police.
52-year-old Sunanda was found dead in her suite at a five-star hotel in south Delhi on the night of January 17, 2014, a day after she was involved in a spat with Pakistani journalist Mehr Tarar on micro-blogging website Twitter over the latter’s alleged affair with Tharoor.